The present invention relates to a swiveling type plastic working machine such as a press-fitting or caulking machine and a rotary forging machine. More particularly, the invention relates to a swiveling type plastic working machine for pressing against a workpiece a molding die mounted on a molding die holder having a slanted axis intersecting with a vertical axis in the vicinity of a working portion, while swiveling the molding die holder about the vertical axis, thereby performing a plastic working to the workpiece. The term "swiveling" used herein means a circular rocking motion of a die with respect to the workpiece.
A conventional swiveling type plastic working machine of this type has been generally used as a "forging" machine for performing a "forging" work with plastically deforming a head of a rivet. The "forging" work is performed for the purpose of forming the head of the rivet into a simple flat shape or a simple curved shape and has hardly been used for forming a complicated shape. Also, in a rotary forging machine, it is common that a stationary lower molding die serves to form a complicated shape and a swiveling upper molding die is used for filling a workpiece into the lower molding die. Therefore, the surface worked by the upper molding die is of a simple flat configuration.
Accordingly, no particular attention has been drawn to a slippage between the dies and the workpiece, and the slippage is simply and incompletely avoided only by the frictional force naturally provided between the dies and the workpiece. For example, Japanese Utility Model Publication No. 55-38601 shows an arrangement in which a die is mounted on a shaft to be rotatable about its own axis so that the die may be rotated in accordance with the contact friction between the die and the workpiece.
Further, in the case where the head having a complicated shape is plastically machined by the machine of this type, an attempt has been made in which a pin is implanted in the molding die or the molding die holder so that the pin is brought into contact with a frame of the machine, or otherwise the pin is engaged with a vertical groove formed in the frame so that the complicated shape formed in the molding die surface is exactly translated to a surface of the workpiece.
Also, there has been proposed an arrangement in which two keys are used for the purpose of preventing a main shaft from being rotated during the swiveling operation.
However, it is impossible to control the revolving position of the die about its own axis with the former free revolving system which uses the frictional force. Therefore, in the case where a mold pattern is formed in a molding die (upper molding die), it is impossible to keep constant a rotational positional relation with the other molding die (lower molding die). It is thus impossible to use the free revolving system.
Also, the latter system in which the revolving operation is restricted by a pin or key suffers from a problem such that it is impossible to change a swinging or swiveling center of the upper molding die.
Further, in such a working operation, there is not only a case where any slippage between the dies and the workpiece is absolutely eliminated for forming a complicated molded surface but also another case where a controlled slippage therebetween is intentionally provided for additionally enhancing a surface roughness of the workpiece greater than that of the dies in, for example, spinning works. Accordingly, there has been a demand to realize the machine that is usable for both purposes. Related U.S. Pat. applications have been filed bearing Ser. No. 227,301 filed on Aug. 2, 1988, and Ser. No. 436,032 filed on Nov. 14, 1989.